We will study the properties of the tail protein of phage P22 and investigate how these properties can be altered by mutagenesis and chemical modification. To accomplish this mutants which synthesize abnormal tail protein will be isolated and mapped. Each mutant protein will be isolated and tested for the three known tail protein functions: head binding, cell binding, and o-antigen hydrolysis. Chemically modified proteins will be tested in the same way. By thus gathering genetic, biological, and biochemical data on the same protein specie, we should gain new insights into the mechanism of action of multifunctional proteins. We will also study those steps in P22 assembly which can be demonstrated in vitro. To this end, phage particles bearing multiple conditional lethal mutations will be exploited for their capacity to direct the synthesis of incomplete phage particles. Infections with multiple mutants will also be used as a source for the morphogenetic proteins necessary to complete the assembly of the unfinished particles. Plaque forming ability will be the sole criterion for successful assembly of the phage particle.